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Arif Ullah khan utman kheel
this is because for conductor E parallel is zero this means that the surface of the wave guide is at equipotential and this potential follow the laplace equation .it means that there is no maxima and minima inside the wave guide . this means that the electric field inside zero . hence the TEM do not exist in wave guide only TE and TM can be exist . if we place some conductor in the wave guide then the conductor inside will not be equipotential and the TEM waves can be exist . like in Coaxial cables
What else can I help you with?
Why TEM mode does not exist in waveguide?
for TEM u need to a magnetic field (H) linked to an electric field .for this u need to a J relative to E (E=sigma J). because [curl H = J] but optical fiber is dielectric wave guide and sigma is zero and u only have dD/dt so there isn't H linked to E.
What is difference between Rectangular Waveguide and Circular Waveguide?
circular is easy to manufacture than rectangular As the name indicates the circular is circular in shape and rectangular is rectangular in shape its uses same modes that is Te and Tm I know this much only hope this helped u little bit atleast A: In principle waveguides act as the equivalent of wires for high frequency circuits. For such applications, it is desired to operate waveguides with only one mode propagating inside of the waveguide. With rectangular waveguides, it is possible to design the waveguide such that the frequency band over which only one mode propagates is as high as 2:1 (i.e. the ratio of the upper band edge to lower band edge is 2). With circular waveguides, the highest possible band width allowing only a single mode to propagate is only 1.3601:1. I found it on Wikileaks.
What is the dominant mode of propagation in microstrip line in low frequency approximation?
quasi-TEM
What is motoring mode of DC motor?
Read this Part I:DC Motor principles pg 1 Part I: Principles of DC Drive Control Learning Objectives: * to learn the basic characteristics of DC motors and their control parameters * to understand the various operating modes DCmotors and their representation: The basic principle of a DCmotor is the production of a torque as a result of the flux interaction between a "field" produced on the STATOR (either produced by a permanent magnet, or a field winding) and the current circulating in the "armature" windings on the ROTOR. In order to produce a torque of constant sign, the armature winding loops are connected to a set of "brushes" which commutate the current appropriately in each loop according to their geometric position. The commutator is a MECHANICAL RECTIFIER. Note that reversal of either the field current or the armature current results in a torque in the opposite direction. However, reversal of both fields does not change the torque direction, hence it can be used as a "universal motor" with DC or AC feed if both windings are in series. Basic Equations of a DC Machine: Steady state conditions (assume all time varying quantities have a constant average value) ( ) ( ) ( ) ( ) ( ) P T developed power T K I I A B T electrical torque V R I E R I K I armature voltage E K I Counter emf or Back EMF V R I fieldwinding d e e t f a load a a a a a v f v f f f f w w w w = = = + + = + = + = = (The back emf assumes that the magnetizing characteristic, E(If) is linear) Speed control: we can extract: v f a a a K I V - R I w = and one can control the speed with 1) Va "Voltage Control" 2) If "Field Control" 3) Ia (with If fixed) "Demand Torque" In practice, for speeds less than the base speed (rated), the armature current and field currents aremaintained at fixed values (hence constant torque operation), and the armature voltage controls the speed. For speeds higher than the base speed, the armature voltage is maintained at rated value, and the field current is varied to control the speed (note the hyperbolic characteristic). However, N +V (free wheeling diode) Armature Current (Rf, Lf) (La, Ra) Eo Rfc Field Control Resistor Fig 1: DC Motor Part I:DC Motor principles pg 2 this way the power developed Pd is maintained constant. This mode is referred to as "field weakening" operation. Case of Series Motor (or Universal Motor) In this case the field winding is series with the armature winding, hence If and Ia are equal. This leads to: v a a a f a K I V - (R + R )I w = One can either control the armature voltage (Voltage Control), or the armature current (Current Control) which is a measure of the torque control. Td , Pd Torque Power constant torque constant power speed Ia If Fig 2: Control Modes Torque Power constant torque constant power speed Td Ia Fig 3: DC Series Motor Control Part I:DC Motor principles pg 3 OperatingModes of DCMotors: Motoring: The back emf E < Va both Ia and If are positive. The motor develops a torque to meet the load torque. Dynamic Breaking: The voltage source is removed, and the armature is shorted. The kinetic energy stored in the rotor of the motor is dissipated in the armature resistance since the machine now works as a generator. Note here that theoretically, since the armature voltage is proportional to the speed, the motor would never stop... but in fact because there is also friction and viscous friction (windage), the motor will stop as soon as the speed is at a certain low value. Regenerative Breaking: The back emf E > Va , the machine acts as a generator, and the armature current flows towards the source, hence energy stored in the machine rotor is fed back to the source. Note however that this will cause the machine to slow down usually until E=Va and then revert to mode 1. Plugging: Plugging iswhen the field current is reversed, hence the back emf changes sign, and the equation of the machine becomes: a a a V = -E - R I hence a a a R I V E + = which means a very high torque generated in the opposite direction of rotation. Avery powerful breaking takes place. However it must be noted that the armature has to be opened as soon as the motor reaches zero speed, otherwise it will start rotating in the opposite direction. N +Va Rfc (La, Ra) E Ia (Rf, Lf) +Vf If Fig 4: Motoring Forward Tem w rated torque V1 V2 V3 V2 Tload FIG 5 torque speed V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 6: Dynamic Breaking + Ia R V2 N +Va Rfc (La, Ra) E (Rf, Lf) +Vf Fig 7: Regenerative Breaking + Ia Part I:DC Motor principles pg 4 Two Transistor control of regenerative operation When the main switch opens, the armature current I(a1) has to be dissipated through the freewheeling diode. Then if one closes switch T1, the machine behaves as a generator with the energy stored in its inertia. Therefore the armature current I(a2)will start flowing and follws I(1). After a certain time one opens the switch T1, and the current I(a2) has to be redirected via diode D2 back to the source with I(2). This is because of the inductance of the machine acts as an emf restoring the flux stored in the magnetic field. Then one closes T1 again and so on. The chopping rate of switch T1 can be set in order to control the average current (Ia2), usually 1.5 times rated value. This is possible only if the speed is fast enough to provide terminal voltage. When the emf E reaches E=Ra.I(rated), the switch T1 remains closed for maximum breaking possible with the given emf. Four Quadrant Operation: Figure 8 summarizes the modes of operation in a four quadrant representation. Torque Speed Forward MOTORING Forward BREAKING Reverse BREAKING Reverse MOTORING Fig 8: 4 quadrant operation V2 N +Va (La, Ra) E Fig 7: Regenerative Control + T1 i2 i1 ia1 ia2 average Ia
The waves which cannot be transmitted in waveguide are?
The waves that cannot be transmitted in a waveguide are those that have a wavelength longer than the cutoff wavelength of the waveguide. These waves are unable to propagate efficiently within the waveguide due to the cutoff phenomenon which restricts their transmission.
Why TEM waves cannot propagate in a wavwguide?
In a waveguide, transverse electromagnetic (TEM) waves cannot propagate because they require both electric and magnetic field components to be present and perpendicular to the direction of propagation. In a waveguide, the fields are constrained to be transverse to the direction of propagation, which is not possible for a pure TEM wave.
Which wave cannot exist inside wave guide?
TEM TE modes (Transverse Electric) have no electric field in the direction of propagation. * TM modes (Transverse Magnetic) have no magnetic field in the direction of propagation. * TEM modes (Transverse ElectroMagnetic) have no electric nor magnetic field in the direction of propagation. * Hybrid modes are those which have both electric and magnetic field components in the direction of propagation
Why TEM wave cannot propagate thorough a rectangular waveguide?
TEM modes (Transverse ElectroMagnetic) have no electric nor magnetic field in the direction of propagation. In hollow waveguides (single conductor), TEM waves are not possible, since Maxwell's Equations will give that the electric field must then have zero divergence and zero curl and be equal to zero at boundaries, resulting in a zero field. BY JITONJA GOGO at THE UNIVERSITY OF DODOMA
Why TEM mode does not exist in waveguide?
for TEM u need to a magnetic field (H) linked to an electric field .for this u need to a J relative to E (E=sigma J). because [curl H = J] but optical fiber is dielectric wave guide and sigma is zero and u only have dD/dt so there isn't H linked to E.
Why TEM modes does not exist in wave guides?
Arif Ullah khan utman kheel this is because for conductor E parallel is zero this means that the surface of the wave guide is at equipotential and this potential follow the laplace equation .it means that there is no maxima and minima inside the wave guide . this means that the electric field inside zero . hence the TEM do not exist in wave guide only TE and TM can be exist . if we place some conductor in the wave guide then the conductor inside will not be equipotential and the TEM waves can be exist . like in Coaxial cables
What is difference between Rectangular Waveguide and Circular Waveguide?
circular is easy to manufacture than rectangular As the name indicates the circular is circular in shape and rectangular is rectangular in shape its uses same modes that is Te and Tm I know this much only hope this helped u little bit atleast A: In principle waveguides act as the equivalent of wires for high frequency circuits. For such applications, it is desired to operate waveguides with only one mode propagating inside of the waveguide. With rectangular waveguides, it is possible to design the waveguide such that the frequency band over which only one mode propagates is as high as 2:1 (i.e. the ratio of the upper band edge to lower band edge is 2). With circular waveguides, the highest possible band width allowing only a single mode to propagate is only 1.3601:1. I found it on Wikileaks.
What is TE and TM modes?
Transverse electromagnetic (TEM) is a mode of propagation where the electric and magnetic field lines are all restricted to directions normal (transverse) to the direction of propagation. Plane waves are TEM, however, we are more interested in what types of transmission lines can support TEM.
Why the both electric and magnetic field are don't exist in the direction of wave propagation in tem waves?
In TEM (transverse electromagnetic) waves, the electric and magnetic fields are perpendicular to each other and perpendicular to the direction of wave propagation. This is because the wave is designed to have components that oscillate in orthogonal planes, allowing the wave to propagate without the need for a medium to carry it.
What is the explanation for the principles of electromagnetic wave?
An electromagnetic wave is properly called a Transverse Electro Magnetic wave, or TEM wave. It consists of an alternating magnetic wave at right angles to an alternating electric wave, with both fields being at right angles to the direction of propagation. The plane of the electric field is defined as the plane of polarization.
How do you spell 'has' in Portuguese?
He has - Ele tem She has - Ela tem
What are the characteristics of a TEM wave?
In a TEM wave, both the E and H vectors are perpendicular to the direction of power flow, represented by 'S', the Poynting vector, which in turn is simply the direction in which the wave is travelling. So neither has any component in the direction of propagation. But are E and H necessarily perpendicular to one another? Ex.: P = Pz ẑ E = Ex x + Ey ŷ H = Hx x + Hy ŷ
